…Mursa (modern Osijek, Croatia), where on September 28, 351 emperor and usurper meet in battle.

Constantius before the battle had set Flavius Philippus, his Eastern Praetorian prefect, to negotiate with Magnentius, requiring the usurper withdrawal to Gaul.

After this inconclusive mission, one of Magnentius’s commanders, Silvanus, and his men had deserted to Constantius.

Magnentius leads his troops into combat; Constantius leaves the battlefield to preach on the nearby tomb of a martyr.

Constantius' army is outnumbered, but after prolonged fighting his cavalry routs Magnentius' right wing, and soon his victory is complete.

The battle entails major losses on both sides, leaving the two strongest armies of the empire—those of Gaul and of the Danube—massacred, thus severely crippling the military strength of the Roman Empire and compromising its defense.

Known as the bloodiest battle of the century, it is also the first defeat of Roman legionaries by heavy cavalry.

Losses suffered by the victors (thirty thousand) exceed those of the routed force (twenty-four thousand), however.

Magnentius flees the field and retreats to northern Italy to regroup his forces.